The present invention relates to a monitoring system for a hybrid fiber cable (HFC) communication network and, more particularly, to the use of a plurality of xe2x80x9ctest pointsxe2x80x9d, distributed through the network topology to locate and isolate sources of noise (such as ingress) within the network.
Modem cable systems utilize a hybrid fiber cable (HFC) architecture in which signals are distributed via a fiber optic connection to a node which converts the optical signal to an electrical signal and distributes the signals to residences via a tree and branch coaxial cable distribution network (xe2x80x9cplantxe2x80x9d) consisting of the coaxial cable, amplifiers and taps. The plant can be made bi-directional through use of a fiber optic return signal from the node to the head end. A return band, typically from 5-42MHz, is used to support transmission from devices in the home back to the head end. Transmissions from the residences are received at the node, converted to an optical signal, and transmitted to the head-end on a separate return fiber or on a return wavelength separate from the downstream wavelength.
An ideal bi-directional cable network can be defined in terms of several characteristics including, but not limited to, the ability to suppress undesirable energy in the network, the ability to identify undesirable energy sources, the ability to thwart or otherwise reduce the likelihood of pirates in the network, high shared bandwidth efficiency, quality of service reliability, flexible bandwidth allocation and network sharing.
Suppressing undesirable energy in an HFC network is an important characteristic when operating a network having a bi-directional communication path on a shared wire between a headend and each of a plurality of remote points. One technical challenge is to maintain adequate network integrity for signals being transmitted simultaneously in the forward path and return path directions so that signals are not contaminated and do not require retransmission. xe2x80x9cIngressxe2x80x9d is defined as unwanted energy that enters a communication path from a source external to the communication path. Ingress presents one of the greatest problems in a network since the unwanted signal is often an impulse noise that enters the network at a weak point, where these weak points are all too often at or near a remote point where there is a shield discontinuity, a poor shield, or a faulty connector. Radio frequency carriers from shortwave radio, citizen""s band radio, or other broadcast sources may also enter the network at these weak points and cause interference peaks at specific carrier frequencies in the communication path. Another ingress source is impulse noise consisting of high power, short duration energy pulses. The high power energy pulse results in a significant rise in the noise floor while the short duration results in an elusive disruption whose source or entry point is difficult to pinpoint.
Thus, a need remains in the art for an arrangement capable of recognizing and isolating sources of noise (e.g., ingress) in an HFC network without impacting the performance of the entire network.
The need remaining in the prior art is addressed by the present invention, which relates to a monitoring system for a hybrid fiber cable (HFC) communication network and, more particularly, to the use of a plurality of xe2x80x9ctest pointsxe2x80x9d, distributed through the network topology, to locate and isolate sources of noise (such as ingress) within the network.
In an exemplary embodiment of the present invention, a set of test points are disposed at the xe2x80x9ctopxe2x80x9d of each branch, between a series of endpoints and the cable mode test system (CMTS). One function performed by the CMTS is to monitor the return signals (upstream) and compare the bit error rate (BER) of each return signal against a predetermined threshold. When the threshold is exceeded, an alarm signal (including the identity of the nearest test point) is sent to a network management system. The network management system then communicates with the test point nearest the noise source to either xe2x80x9cisolatexe2x80x9d that part of the network or actively alter the performance of the network to mitigate the noise problem.
In one embodiment, a set of active notch filters may be used as the test points, with the capability to move the center frequency of a filter to block a particular source of ingress noise from progressing upward through the network. In an alternative embodiment, a scanning receiver (or set of receivers) may be used to monitor a set of channels reserved for upstream transmission and thus block any particular channel experiencing ingress noise.
Other and further embodiments of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings.